#### Answer

$80$ board feet

#### Work Step by Step

RECALL:
Number of Board Feet = $\dfrac{\text{number of boards} \times \text{thickness} \times \text{width} \times \text{length}}{12}$
where thickness, width, and length are all in inches.
Using the formula above gives:
Number of Board Feet = $\dfrac{10 \times 2 \times 4 \times 12 }{12}=80$